In 3GPP (3rd Generation Partnership Project), which is a project aiming to standardize a mobile communication system, specifications are being designed to enhance LTE (Long Term Evolution) in order to comply with the rapidly increasing traffic demands (for example, see Non Patent Literature 1).
On the other hand, attention is being paid to a specific frequency band that is shared by a plurality of mobile network operators or a plurality of communication systems. Such a specific frequency band includes, for example, an “unlicensed band” and a “licensed shared band”.
Here, an unlicensed band is a frequency band that can be used without a license. A licensed shared band is a frequency band that is allocated for users having one purpose (called “primary users of a frequency”); however, depending on geographical conditions or technical conditions, a licensed shared band is a frequency band that can also be used by users having some other purposes (called “secondary users of a frequency”).
Here, as a means for complying with the rapidly increasing traffic demands in a mobile communication system, the use of the above-described specific frequency band in mobile communication is considered.